An average cord of wood, depending on the efficiency of combustion and wood type, will yield approximately twenty pounds of ashes or the equivalent of one five-gallon pail. Over the winter, this can add up to quite an accumulation of wood ashes. Wood ash acts on the soil in much the same way as limestone, raising the pH, or alkalinity, of the soil. Many wood stove users dump the ashes in their garden with the intention of improving the soil condition of their garden. However, unlike limestone, which can take six months or more to altar the pH of the soil, wood ash has high water solubility and changes the soil pH very rapidly. This may cause problems, as a soil pH over the optimum level can affect plants as adversely as a pH that is too low. High pH will limit the uptake of important soil nutrients needed by the plant such as phosphorous, iron and magnesium.

A safe rate of wood ash application for a garden or lawn area is twenty pounds per thousand square feet (one five-gallon pail full of wood ash). Twenty pounds of wood ash is equivalent to six pounds of ground limestone per thousand square feet. If the soil is in the proper pH range, this rate of application is considered appropriate for yearly treatments. The wood application also supplies potassium to the soil. Be sure to mix the wood ash into the soil thoroughly.

It is important to have your soil tested at least once every two years in order to accurately gauge the requirements of your specific soil(s). Refer to the GreenShare Factsheet on soil testing for more information on soil testing.

Adapted from George W. Hamilton, University of New Hampshire Cooperative Extension, 2000